Page 356 - Offshore Electrical Engineering Manual

CHAPTER

Notes on Offshore 6

Renewable Energy

Substation Platforms

INTRODUCTION
Large marine renewable energy projects such as wind and wave farms located off-
shore will generally require an offshore platform for power equipment to act as a
collection node for the generator cables operating at medium (generating) voltage,
the step-up transmission transformers and the necessary switchgear. The platform
may not have to be continuously manned for operation of the renewable farm, but
temporary manning will be required for maintenance purposes.
Where such platforms are close inshore, small service vessels can be used to ferry
personnel and equipment out to them, and access is usually by ladder and harness.
However, if the platform is far offshore, boat access becomes time consuming and
hazardous, and the platform will need to be equipped with a helideck.

DESCRIPTION

A typical wind farm in UK waters may consist of 200 wind turbines. For the pur-
poses of the substation hub, the turbines would be grouped into 10 groups of 20,
with a main 33-kV cable from each group connected to the hub platform. Each 50%
capacity transformer outputs to metalclad SF6 outdoor type switchgear to a 132-kV
subsea cable.
Main uninterruptible power supply (UPS) batteries would be typically
2 Ah × 200 Ah banks and would preferably be located in a separate battery room or
enclosure.
The current UK Maritime and Coastguard Agency guidance document is MGN
543 (M + F) see UK Maritime and Coastguard Agency.
Substation platforms are usually unmanned except for normal summer mainte-
nance campaigns and emergency visits.
The main transmission cables (both 33 and 132 kV) would normally have fibre-
optic cores for both communications and telemetry.
The (exposed) transformer coolers should be protected from damage due to
dropped objects, whilst maintaining cooling airflow.
A standby/emergency generator should be provided to supply power for lighting
and utilities and to maintain UPS battery charge for telecommunications and control
systems, when the utilities transformer is unavailable.

Offshore Electrical Engineering Manual. https://doi.org/10.1016/B978-0-12-385499-5.00039-X 343
Copyright © 2018 Elsevier Inc. All rights reserved.